A runway refers here to a surface on which an object may travel. In the vertical direction, the runway thus comprises a plane that is substantially perpendicular to the ambient gravitational force. Typically the runway also comprises some mechanism that eliminates possible lateral forces to allow progress of the object along the runway.
A well known example of a runway is a rail system that may comprise one, two or more rails, mounted on the ground such that their top surface is substantially perpendicular to the ambient gravitational force. Rail systems are surveyed periodically to ensure the dimensions of the rails are within established geometrical values (standards). Data generated during the survey is then utilized to correct the positioning of the rails if there is any deviation.
Traditionally runway surveys have been performed with manual arrangements that apply theodolites or lasers. Recent years have brought in use a tachymeter that can be fixed to one position while a target moves longitudinally along a rail to predefined measuring positions. By measuring the coordinates and distance of the target, the values needed to compute dimensional characteristics of the rail defined in the runway standards (for example span, rail to rail elevation, elevation and straightness) can be directly determined.
Recently, a number of automated measuring systems have been introduced. Document US 2005/0111012 discloses a laser survey device, which uses a remotely operated laser to perform a runway survey The laser survey device includes a stationary component, that includes a self-leveling laser, and a mobile component, that includes a screen and an image capture device. In operation, the stationary self leveling laser emits a beam of laser light towards the screen of the mobile component as the mobile component travels along the length of a crane rail. As the mobile screen travels along the length of the crane rail, the location of impact of the laser light on the mobile screen changes depending on movement of the mobile screen within a plane perpendicular to the steady beam of laser light emitted by the stationary, self leveling laser. The image capture device captures and transmits to a remote computer information related to location of impact of the laser light on the mobile screen. The remote computer uses the received information to assess alignment of the crane rail.
U.S. Pat. No. 6,415,208, describes a laser-based survey device that is very similar, in both design and operation, but is configured to collect alignment data for top-rail crane rail configuration.
Document WO 2007/087317 describes a method and apparatus for conducting an overhead crane runway system survey by using a survey apparatus that is alternately pushed or pulled by an overhead crane.
Document EP2017574 discloses a arrangement for measuring a rail that comprises a fixed tachymeter and a mobile reflecting surface. The measurement comprises determining the position of the mobile element and transmitting the measurement results over the air interface to a computer for further processing.
The problem with any of these automated solutions is deficient accuracy of the results. Rails may have local structures that disrupt the otherwise substantially linear dimensions of the rail. In time and use the rails also wear and the surface on which the moving target travels begins to comprise deformations. These structures caused by deformations and/or local structures are in the following called jointly as defects, and they may cause the measuring elements to diverge from their initial, planned spatial configuration. This spatial configuration is, however, a basis for computing equations and algorithms used in determining the surveyed result values. When the spatial configuration between the separate elements changes, the results become distorted. The reliability of the measured values is thus uncontrollably dependent on the state of the measured track, which is not acceptable.